Solenoid operating circuits



March 17, 1959 R, S, HULL 2,878,431

SOLENOID OPERATING CIRCUITS Filed Dec. 14, 1955 i IT INVENTOR ROGER S. HULL HIS ATTORNEYS ,tive.

United States Patent SOLENOID OPERATING CIRCUITS Roger S. Hull, Dayton, Ohio, assignor to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Application December 14, 1955, Serial No. 553,136 4 Claims. (Cl. 317-1555 This invention relates to a solenoid operating circuit and in particular relates to a circuit having a high initial current, low sustaining current and rapid recovery characteristics.

The novel circuit is arranged to provide a high initial surge of current to a solenoid, when the circuit to the solenoid is closed, so that the solenoid will be energized quickly, and to thereafter cut the current down to maintain the solenoid energized without overheating. This circuit is capable of rapid repeated operation to energize the solenoid under control of a switch.

It is an object of the invention to provide an improved operating circuit for a solenoid.

A further object of the invention is to provide an operating circuit for a solenoid, which circuit will provide a high initial current which will be automatically reduced to allow the solenoid to remain operated without overheating.

Another object of the invention is to provide a novel operating circuit for a solenoid which can cause the solenoid to operate and can be ready to cause another operation of the solenoid after a minimum of recovery time.

A further object of the invention is to provide an operating circuit for a solenoid, which circuit is arranged to provide safe operating conditions and long life for the components in the circuit.

With these and other incidental objects in view, the invention includes a novel circuit arrangement which is hereinafter described with reference to the drawing which accompanies and forms a part of this specification.

The drawing shows the novel operating circuit.

, The circuit is extremely simple but is very eifective to produce the desired operation of the solenoid L.

Beside a capacitor C of 2000 microfarads, the operating circuit only includes a relay having a high impedance winding R of fifty ohms and a low impedance winding R of one-half ohm mounted on a common magnetic circuit, and having a contact R which is normally closed but opens whenever the flux ,in the magnetic circuit reaches a value to cause the relay to operate. The mag netic fields of the windings R and R are additive. As

shown inthe drawing, the windings R and R are wound in the same direction, but it is obvious that these windings could, if desired, be wound in opposite directions and still be connected so that their magnetic fields would be addi- A suitable D. C. operating potential is appliedto terminals and 11.

The two windings R and R are connected in series between terminal 10 and one side of a normally open switch S which controls when the solenoid L will be energized. The solenoid L, in the illustrated embodiment, has a 10-ohm D. C. resistance. This value, however, is not critical, since a change in it produces only relatively slight eflects on the timing of the present circuit. For example, a solenoid L having a D. C. resistance of ohms has also been used successfully in this circuit. The other side of the switch is connected to the solenoid L and thence back to the other terminal 11. A shunt is closed around the winding R by the normally closed contacts R and the capacitor C is connected across the winding R the switch S and the solenoid L.

With the switch S open, the capacitor C will be charged to the full supply potential across terminals 10 and 11 and the shunt will be closed around the high impedance winding R The circuit is now in condition to provide the desired operation of the relay.

When the switch S is closed, current is initially supplied to the solenoid L from two sources, from the D. C. supply via the shunt and from the charged capacitor. The current from the two sources passes through the low impedance winding R switch S and the solenoid L to the other side of the line. These two currents will insure a high initial current through the solenoid L to cause its rapid energization.

The current through the winding R will try to build up flux in the magnetic circuit of the relay but the short-circuited winding R will oppose the flux build-up for a period of time determined by the rate increase of flux through the winding R As soon as the rate of flux change is reduced, the effect of the short-circuited winding is reduced and the flux in the circuit will be suflicient to operate the relay to open contacts R which open the shunt around the winding R to place the fifty-ohm winding R in series between the terminal 10 and the combination of capacitor C and solenoid L. This inhibiting action of the shorted winding R delays the relay operation sutficiently to insure that the solenoid L will have been energized before current thereto is reduced.

With winding R also efiectively in the circuit, the current which is supplied to the solenoid L is reduced to a value which will not cause undue heating for more or less sustained operation.

Accordingly, with the closure of the switch S, the solenoid L will be supplied with a high initial energizing current to cause rapid operation and will then automatically be supplied with a lower sustaining current until the switch S is opened.

While the solenoid remains energized the capacitor C will not be charged to the full potential of the D. C. supply but to a lower potential due to the drop across the relay winding R When switch S is opened to deenergize solenoid L, current will continue to flow from the power supply through the winding R to build up the charge on the capacitor C, tending to restore the potential across the capacitor to that of the source.

It is noted that the SO-ohm impedance is effective to prevent too great a surge in the charging rate when the switch S is opened, and thus, protects the capacitor. The charging of the capacitor is exponential and becomes slower as the potential across the capacitor approaches the supply potential. When the current flow through the winding R is reduced to a point where the flux resulting therefrom will no longer hold contacts R open, these contacts reclose to complete the shunt around the winding R and apply the full D. C. supply potential across the capacitor to accelerate its recharging to the full D. C. supply potential in preparation for another operation of the solenoid. I v

The novel circuit not only is capable of supplying a high initial current to operate the solenoid and thereafter automatically supplying a lower sustaining current. but also is capable of rapid recovery which enable the solenoid to be operated repeatedly at a relatively high rate.

While the circuit shown and described herein is ad-- mirably adapted to fulfill the objects primarily stated, it is to be understood that it is not intended to confine: the invention to the particular form and values of com-- in aiding relation and having normally closed contacts which are opened when the relay is operated, a capacitor.

and a load; said circuit extending from one of said terminals-over said high impedance winding, then over the low impedance winding in series, and over the load to the other terminal, with the junction between the windings connected over the capacitor to the other terminal, and with a shunt connection, including said relay contacts, shorting out the high impedance winding until the relay is operated; and said circuit supplying an initial high current and automatically, 2. low sustaining current to the load, and recovering rapidly after each use.

2. A circuit having high initial current, low sustainiing current and rapid recovery characteristics, including a pair of terminals to which a D. C. operating potential may be applied, a double wound relay having a high impedance operating winding, 2. low impedance operating winding in aiding relation and normally closed contacts which are opened when the relay is operated, a power storage capacitor, and a load; said circuit extending from one of said terminals over said high impedance winding,

then over the low impedance winding, and over the load to. the other terminal, with a shunt, including said relay contacts, shorting out the high impedance Winding until the relay is operated and with a connection from the junction of the windings over the capacitor to the other terminal to cause the capacitor to be charged to the D. C. operating potential until the load is connected to the circuit; said circuit being effective, when the load is connected between the low impedance winding and said other terminal, to supply an initial high current to the load. over said low impedance Winding to operate the relay, after a predetermined delay period, to open the shunt and render the high impedance winding effective in the circuit to automatically reduce the current to the load; and Said high impedance winding, when effective, also maintaining the relay operated after the load has been removed and until the capacitor has been partially recharged, at which time the relay is released and the full D. C. operating potential is applied across the capacitor to rapidly complete its recharging.

3. A circuit having high initial current, low sustaining current and rapid recovery characteristics, including in combination, a pair of terminals to which a D. C. operating potential can be supplied, a relay having a high impedance operating winding, a low impedance operating winding in aiding relation and normally closed contacts which are opened when the relay is operated; a power storing capacitor; a solenoid which is to be energized by the circuit; and a control switch which is closed when the solenoid is to be energized; said circuit extending from one of the terminals, over the high impedance winding, then the low impedance winding in series to one side of the switch and from the other side of the switch over the solenoid to the other terminal, and including a shunt connected across the high impedance winding over the normally closed relay contacts to short out the high impedance winding from the circuit until the relay operates, and further including a connection from the junction between the windings, over the capacitor to the other terminal to enable the capacitor to be charged normally to the full D. C. operating potential; the closure of the switch causing an initial energizing current from the charged capacitor and the D. C. supply to be applied to the solenoid over only the low impedance winding to provide a high initial energizing current to the solenoid and to cause the relay to operate and remove the short from across the high impedance winding to include the high impedance winding in the circuit; said shorted high impedance winding delaying the operation of the relay; and said high impedance winding, when included in the circuit, reducing the current supplied to the solenoid and also maintaining the relay operated and the shunt open until after the switch is opened and the capacitor is nearly recharged, at which time the relay is released and the shunt reclosed to apply the full D. C. potential to the capacitor to quickly complete the recharging thereof.

4. A solenoid operating circuit including a pair of terminals to which a D. C. operating potential is supplied; a relay having a high impedance winding, a low impedance winding in aiding relation and a normally closed contact which is opened when the relay is operated; a large capacitor; a solenoid which is to be operated by the circuit and a normally open control switch which is closed when the solenoid is to be energized; said circuit extending from one of said terminals, over the high impedance winding, then the low impedance winding in series to one side of the switch from the other side of the switch over the solenoid to the other terminal and said capacitor being connected in shunt across the low impedance winding, the switch and the solenoid and normally charged to the full D. C. operating potential when the switch is open, and a further shunt connected across the high impedance winding and including the normally closed relay contacts to short out the high. impedance winding from the circuit until the relay operates, the closure of the switch causing an initial energizing current from the charged capacitor and D. C. supply to be applied to the solenoid over only the low impedance winding to provide a high initial energizing current to the solenoid and to cause the relay to operate and remove the short from across the high impedance winding to include the. high impedance winding in the circuit and thereby reduce the current supplied to the solenoid; said high impedance winding maintaining the relay operated and the shunt open after the switch is opened and while the capacitor is recharging until the capacitor is nearly charged, at which time the relay is released and the shunt reclosed to apply full D. C. potential to the capacitor to quickly complete the recharging thereof.

References Cited in the file of this patent UNITED STATES PATENTS 954,745 Larsen Apr. 12, 1910 1,172,962 Eaton Feb. 22, 1916 1,810,306 Trofimov June 16, 1931 1,917,418 Almquist July 11, 1933 2,427,751 Snyder Sept. 23, 1947 

